1. Field of the Invention
The present invention relates in general to a hydraulically operated braking system, and more particularly to a hydraulically operated braking system including an assisting device for boosting a drive force to be applied to a pressurizing piston of a master cylinder.
2. Discussion of the Related Art
An example of a hydraulically operated braking system including such an assisting device as described above is disclosed in JP-A-4-328064. This braking system includes (1) a master cylinder having a pressurizing piston operatively connected to a brake operating member to pressurize a working fluid in a pressurizing chamber, (2) a brake cylinder for actuating a brake device based on the pressure of the pressurized fluid, and (3) an assisting device for applying to the pressurizing piston an assisting drive force which is different than a primary drive force to be applied to the pressurizing piston on the basis of a brake operating force acting on the brake operating member. In this braking system wherein the primary drive force and the assisting drive force are both applied to the pressurizing piston, the fluid pressure in the pressurizing chamber can be boosted, permitting the brake device to produce an increased braking force for a given value of the brake operating force. However, the assisting drive force to be generated by the assisting device is simply proportional to the brake operating force. That is, the assisting device disclosed in the above-identified publication is not capable of producing the assisting drive force which is not proportional to the brake operating force.